Lamp base



FIG. 1 is a front elevational view of a lamp base showing my new design, the rear elevational view being identical thereto;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof; and

FIG. 4 is a right side elevational view thereof, the left side elevational view being identical thereto. 

The ornamental design for a lamp base, as shown and described. 